I realized something: I have no idea what I'm doing. I have a little experience in assembly with Odyssey^2 programming. But I still have no idea how to make a sprite appear and move it around. I looked at the Orange and Zelda code and I didn't understand most of it. I understood that in Zelda, it checked for Link's collision detection, but that's about it. I need someone to dumb down the code and just make a barebones, include only what's needed example of how to get a sprite on screen and move it around.
I fixed Marill's eyes. I also made it so when you press A, it displays the word "test" and the game doesn't do anything else.

After hours of trying various things, I finally got a little Marill to move around the test screen. I don't know how, but I did. The thing that bothered me the most was that I unwittingly kept trying to make a tile instead of a sprite. Since the Marill is supposed to be swimming, I don't plan to have any animation for it. Just drawing this in a 16x16 pixel was hard.

Tilemapping has to be enabled, your map that contains the tile needs to be set as the tilemap in use, then you set that position in the map to the tile's index. Tilemaps are different from sprites in that you don't specify an exact position for each tile, they're placed in 8x8 tiles back to back.

In the documentation supplied with PokeMini, check out doc/PM_PRC.html#Map_Rendering_Stage

You don't display the entire map at once. Rather a tilemap is meant to contain unique entries of each tile that can be displayed together. You select which tiles are displayed at any given time by setting the indexes in RAM, which is also the only way to display them. If you want to not display anything, so to speak, you need to have an empty tile in your tilemap.

mov x1,$13C0 ; pick out a tile (the number 0)
mov x2, $1376 ; where i want the tile to be (below "mins)
mov a, [x1]
mov [x2], a
mov x1,$13C0 ; pick out a tile (the number 0)
mov x2, $1377 ; where i want the tile to be (below "mins")
mov a, [x1]
mov [x2], a

How do the pros do scores if they can't use more than one map at a time and you can't choose tiles offscreen?